Prof, von Kohell upon Galvanography. 235 



to the highest Hghts. The shades are laid on according to their 

 depth, and when the picture is completed, these portions are to 

 be farther treated with plumbago, as has been described. The 

 picture thus prepared should be dull on its surface, and should 

 there remain on the thicker portions of the paint any glossy parts, 

 they are to be deadened by a further slight application of the 

 black-lead paint. 



When large portions of the picture are occupied with very 

 deep shades, the following process is necessary. The picture 

 being otherwise complete, the shades in question are to be paint- 

 ed over with some unctuous oil color, (sienna answers very well,) 

 fine black lead powder is to be sieved over the surface, and what 

 does not adhere to those places to be thrown off by giving the 

 plate a few gentle blows. The parts thus prepared present a vel- 

 vety appearance, and enable us to produce the deepest shades 

 with the utmost facility. 



The picture is to be painted upon a finely polished silver-plated 

 copper plate, similar to those used for the Daguerrotype, the 

 color being laid on upon the silvered side. To avoid the un- 

 pleasant glare from this plate, its entire surface, with the excep- 

 tion of the highest lights, may receive, when the picture is sketch- 

 ed in, an extremely thin film of color. 



It must be borne in mind while executing the painting, that 

 the impression obtained from the copper plate always proves 

 somewhat paler than the original, the reason of which does not 

 lie in a want of truth in the copy, but rather in the necessary 

 wiping of the plate, in a certain portion of the ink being absorb- 

 ed by the paper, and so forth. No other colors than those enu- 

 merated are to be used in a painting, and it is detrimental to give 

 the surface of the silver a coat of varnish. 



The method of transferring a design to a plate is as follows. 

 The back of the paper is to receive a coat of dark colored oil 

 paint, which is rubbed in with wool till it no longer soils the 

 fingers, and the picture is then to be pricked through on to the 

 plate with a sharp point of wood or other similar instrument. 



It does not answer to use a pure copper plate instead of a plated 

 one, but a copper plate platinized or coated with silver, as de- 

 scribed under (5), will do very well. Were a simple plate of 

 copper used, there would be a risk of injuring the deposited 

 plate in detaching it from the painted one, especially where many 



